1. Field of the Invention
The present invention relates to a driving mechanism, a photographic mechanism in which an optical member is connected to the driving mechanism such as a small digital camera and a web camera and a cellular phone provided with the driving mechanism and the photographic mechanism.
2. Description of the Related Art
An actuator in which an electro-mechanical conversion element such as a piezoelectric element is used is known as a driving mechanism for a lens used in digital cameras and the like. For example, as shown in the embodiments of Japanese Patent No. 3171187 or Japanese Patent No. 3171022, the actuator is, in general, constituted by an electro-mechanical conversion element and a driving member and fixed to a cabinet (or support member) on one end surface of the electro-mechanical conversion element in the elongation and contraction direction. A driving member is fastened to the other end surface of the electro-mechanical conversion element in the elongation and contraction direction, and a driven member is frictionally engaged with the driving member. The above-described constitution makes it possible to transmit a movement in the elongating and contracting direction of the electro-mechanical conversion element to the driving member when a pulse-form voltage is applied to the electro-mechanical conversion element. Where the electro-mechanical conversion element is deformed slowly, the driven member moves together with the driving member. Where the electro-mechanical conversion element is quickly deformed, the driven member remains at the same position due to inertia of the mass. Therefore, the driven member is allowed to move intermittently at a fine pitch by a repeated application of the pulse-form voltage which is different in reciprocating movement.
Since the thus constituted actuator is fixed to a cabinet (or a support member) at one end surface of an electro-mechanical conversion element in the elongation and contraction direction, in association with vibration of the electro-mechanical conversion element, vibration generated on an actuator including a driving member is directly transmitted to the cabinet, thereby causing a problem that vibration has developed between the actuator and the cabinet.
JP-A-2002-142470 has disclosed a mechanism in which a base is provided between an electro-mechanical conversion element and a cabinet, one end surface of the electro-mechanical conversion element in the elongation and contraction direction is fixed to the base, and the base is elastically supported to the cabinet, thereby reducing or blocking vibration transmitted between the base and the cabinet to avoid the effect of the resonance.
Further, Japanese Patent No. 3171187 has disclosed a mechanism in which a charging time of applying voltage to an electro-mechanical conversion element is made equivalent to about one cycle of resonance frequency of the electro-mechanical conversion element and a discharging time is made equivalent to ½ cycle, namely, resonance is actively used, thereby increasing an elongation and contraction extent of the electro-mechanical conversion element to improve the driving efficiency of an actuator.
In addition, Japanese Patent No. 3171022 has disclosed a method for driving an actuator, with the effect of the resonance taken into account, in which the driving frequency f of the actuator is expressed by f1/3≦f≦2f1/3 where a driving member is fixed to one end of an electro-mechanical conversion element which is kept free and the other end is used as a fixed end to give the resonance frequency as f1.
The mechanism disclosed in JP-A-2002-142470 is to avoid at least the effect of the resonance. Therefore, in the mechanism, the conditions are established for the resonance frequency of an actuator and the driving frequency of an electro-mechanical conversion element in a state that an adverse effect of resonance may develop, unless a base is elastically fixed to a cabinet. Further, since the mechanism disclosed in Japanese Patent No. 3171187 is to make an active utilization of resonance, in any case, there is a problem that an adverse effect by resonance inside an actuator results in displacement of a driving member in a direction other than the elongating and contracting direction of a piezoelectric element. For example, as shown in FIG. 17A and FIG. 17B, such a problem is posed that a driving member 2 is influenced by the resonance to displace in a direction other than the elongating and contracting direction of the piezoelectric element. Therefore, a driving force by the elongation and contraction of the piezoelectric element 1 is not accurately transmitted to a driven member 3, thereby making it difficult to accurately move the driven member 3 in the elongating and contracting direction of the piezoelectric element 1.
Further, in the mechanism disclosed in Japanese Patent No. 3171022 where it is desirable that a constitution system including a cabinet has a resonance frequency higher than a driving frequency, components such as a piezoelectric element and a driving member are made more rigid or individual members are coupled more rigidly to increase the resonance frequency. It is indispensable to make more rigid all the components including the cabinet, which results in a problem that a higher cost is needed in manufacturing the mechanism. There is another problem that according to the conditional expression disclosed in the above Document, since the driving frequency can be established only in a relatively narrow range (in the range shown in Q of FIG. 6B), the resonance frequency is decreased to be deviated from the condition and adversely influenced by resonance, when the mechanism has defects or varies in quality.